a. Technical Field
The present invention relates to hearing devices, and, more particularly, to hearing devices that are deeply positioned in the ear canal with improved energy efficiency, sound fidelity and inconspicuous wear.
b. Description of the Prior Art
(1) Brief Description of Ear Canal Anatomy and Physiology
The external acoustic meatus (ear canal) is generally narrow and tortuous as shown in the coronal view in FIG. 1. The ear canal 10 is approximately 23-29 mm long from the canal aperture 17 to the tympanic membrane 18 (eardrum). The lateral part, a cartilaginous region 11, is relatively soft due to the underlying cartilaginous tissue. The cartilaginous region 11 of the ear canal 10 moves in response to the jaw motions, which occur during talking, yawning, eating, etc. Cerumen (earwax, not shown) production and hair growth occur primarily in the lateral end of the ear canal within the cartilaginous region. The medial part, a bony region 13 proximal to the tympanic membrane, is rigid due to the underlying bony tissue. The skin 14 in the bony region 13 is thin (relative to the skin 16 in the cartilaginous region) and is sensitive to touch or pressure. There is a characteristic bend 15 that roughly occurs at the bony-cartilaginous junction 19. The magnitude of this bend varies significantly among individuals. There is no earwax production or hair in the bony part of the ear canal. The ear canal 10 terminates at the tympanic membrane 18.
A cross-sectional view of the typical ear canal 10 (FIG. 2) reveals generally an oval shape with a long diameter (D.sub.L) in the vertical axis and a short diameter (D.sub.S) in the horizontal axis. The canal dimensions vary significantly among individuals as shown below in the section titled Experiment-A.
(2) The Challenges of Deep Canal Fittings
The benefits of placing a hearing device deep in the ear canal are many. They include improved high frequency response, less distortion, reduction of feedback and improved telephone use (Chasin, M. CIC [Completely In the Canal] Handbook, Singular Publishing, pp 10-11, 1997, referred to hereinafter as "Chasin"). A major benefit for "an invisible hearing device" for the user is cosmetic in nature since hearing aid use is often associated with aging and disability.
A conventional deep canal hearing device 50, shown in FIG. 3, typically includes a battery 52, a microphone 53, an amplifier 54 and a receiver 55 (speaker), among other components (not shown), all of which are housed within an outer shell 51 composed of acrylic or plastic material. The battery enclosure, comprising battery door 56, battery compartment with contacts (not shown), and outer shell 51, is conventionally positioned in the lateral end of the hearing device 50 occupying the lateral end of the ear canal as shown in FIG. 3. The most lateral structure of a hearing device is referred to in the hearing aid industry as the "face-plate" 57 which is attached to the shell 51 and houses the battery door for access to the battery compartment and the battery within (for example, see U.S. Pat. No. 4,272,591 to Brander, U.S. Pat. No. 4,803,458 to Trine et al., and U.S. Pat. No. 5,675,657 to Giannetti).
Since the battery enclosure is a permanent component of a conventional hearing device, the enclosure must be durable to last the life of the hearing device. For this reason alone, the thickness of shells in conventional canal hearing devices typically ranges between 0.5 to 0.7 millimeter (mm).
With continued improvements in miniaturization of hearing aid components, the battery has emerged as the largest single component in miniature hearing devices. For this reason, among others, the battery is typically positioned laterally within the cartilaginous region 11 of the ear canal, a region with relatively larger dimensions as compared with medial regions of the ear canal.
Unfortunately, fitting a hearing device deeper with prior art battery enclosures is virtually impossible for most hearing impaired individuals due to space limitations in the deeper areas of the ear canal. As demonstrated in Experiment-A (described below) employing measurements of ear impressions from human cadavers, the dimensions of the typical ear canal prohibit placement of batteries with conventional enclosures in the vicinity of the bony-cartilaginous junction 19.
Resorting to smaller batteries, and thus a smaller enclosure, to reduce the overall size of the device is not practical for most users who expect a prolonged use of their batteries prior to depletion and replacement.
Another problem associated with battery enclosure in conventional hearing aid designs is caused by the occlusion of the ear canal by the housing of the device. Occlusion related problems include:
(i) Discomfort, irritation and even pain may occur attributable to canal abrasion caused by frequent insertion and removal of an occluding hearing device. Due to canal discomfort and abrasion, hearing devices are frequently returned to the manufacture in order to improve the custom fit and comfort (Chasin, pp. 43-44). "The long term effects of the hearing aid are generally known, and consist of atrophy of the skin and a gradual remodeling of the bony canal. Chronic pressure on the skin lining the ear canal causes a thinning of this layer, possibly with some loss of skin appendages" (Chasin, p. 58). PA1 (ii) The occlusion effect is a common acoustic problem caused by the occluding hearing device. It is manifested by the perception of a person's own-voice ("self-voice") being loud and unnatural compared to that with the open ear canal. This phenomenon is sometimes referred to as the "barrel effect" since it resembles the experience of talking into a barrel. The occlusion effect, which may be experienced by plugging the ears with fingers while talking, is generally related to self-voice resonating within the ear canal. In the ear canal occluded by a conventional hearing device 10 (FIG. 3), a large portion of the self-voice 20, originating from the larynx (voice-box) and conducted upward by various body structures, is directed at the tympanic membrane 18, as shown by arrow 21. Some of the sound energy escapes to the outside through the occluded hearing device as shown by arrow 22. The residual "trapped" sound energy 21 is perceived by the individual wearing the device as loud or unnatural. In the open (non-occluded) ear canal, a relatively larger amount of self-voice 22 is allowed to escape, and the residual sound 21 directed at the tympanic membrane 18 is relatively smaller. This represents what is perceived as natural self-voice. For hearing aid users, the occlusion effect is inversely proportional to the residual volume of air between the occluding hearing device and the tympanic membrane. Therefore, the occlusion effect is considerably alleviated by a deeper insertion of a device within the ear canal.
(3) State of the art in Battery Enclosure in Hearing Devices
As mentioned above, prior art hearing devices typically comprise a battery compartment within an outer shell having an attached face-plate. The shell and the attached face-plate are typically composed of rigid acrylic or plastic material. The shell typically occludes the ear canal.
U.S. Pat. No. 5,201,008 to Arndt et al. describes an open-topped battery compartment (24 in FIG. 1) that is first contained within a first housing (22 in FIG. 1) and subsequently contained in a second housing (12 in FIG. 1, where the Figure numbers mentioned with respect to the patent refer to those in the patent itself). U.S. Pat. No. 5,701,348 to Shennib et al. also describes a battery compartment (15 in FIG. 3) contained in outer housing (13 in FIG. 3) made of rigid non-resilient material. In the above mentioned inventions, the outer housing, containing the battery compartment, is too large to fit in the deeper portion of the ear canal, especially when considering other components (i.e. the microphone) which also reside in the same outer housing.
U.S. Pat. No. 3,701,862 to Vignini, U.S. Pat. No. 5,588,064 to McSwiggen et al., and U.S. Pat. No. 5,687,242 to Iburg all describe a moving battery compartment which activates a switch upon its movement. The combined battery compartment-switch part in the above inventions is space efficient for a hearing device positioned in the outer part of the ear (FIG. 1 of McSwiggen, for example). However, the combined size of the battery compartment, electrical contacts, and enclosing housing similarly prohibits the device from fitting in the deeper portion of the ear canal, particularly at the bony-cartilaginous junction 19 or beyond.
U.S. Pat. No. 4,931,369 to Hardt et al. describes a battery enclosure comprising an electrical contact arrangement within the housing and cover (FIG. 1). Since the battery is housed in a chamber formed by the door and the housing, having dimensions substantially corresponding to the dimensions of the button battery, a battery compartment is eliminated thus providing improved space efficiency.
However, in the disclosure of the '369 patent, as well as the prior art described elsewhere including some of the patents mentioned above, the outer enclosure surrounding the battery also encloses other components such as microphone and amplifier. This contiguous enclosure causes the overall package to increase beyond the dimensions of many ear canals, particularly at the bony-cartilaginous junction and beyond.
It is a principal objective of the present invention to provide a space efficient: battery enclosure for positioning devices deep in the ear canal. Another objective of the invention is to provide an enclosure which minimizes the occlusion of the ear canal.